1. Field of the Invention
The present invention relates to a power supply apparatus such as one designed for use in a vehicle to make it run. More particularly, the present invention relates to a power supply apparatus that uses a battery as an electric power source for driving a load and that incorporates a temperature detection circuit for detecting the temperature of the battery.
2. Description of Related Art
Power supply apparatuses that yield a high output voltage thanks to a plurality of batteries connected in series are used as power supply apparatuses for use in vehicles such as hybrid cars. This type of power supply apparatus incorporates a circuit for detecting the temperature of batteries. When batteries are charged or discharged at abnormally high temperatures, their performance deteriorates significantly. Thus, a power supply apparatus that is so built as to alleviate the deterioration of batteries due to high temperature detects the temperature of the batteries so that, when the temperature becomes higher than a set temperature, the charging or discharging current is limited or even cut altogether to protect the batteries.
There have already been developed power supply apparatuses designed for use in vehicles and incorporating a temperature detection circuit for detecting the temperature of batteries, an example being the one disclosed in Japanese Patent Application Laid-Open No. H11-234801 (hereinafter referred to as Patent Publication 1). The power supply apparatus disclosed in Patent Publication 1 includes a plurality of temperature sensors that are thermally coupled to battery cells. These temperature sensors change their electrical resistances with temperature. Moreover, these temperature sensors are connected in series with one another, and thus, when the temperature of any of the battery cells rises, the serial resistance of the serially connected temperature sensors increases. Hence, by detecting the electrical resistance of the circuit composed of the serially connected temperature sensors, it is possible to detect the battery temperature.
Moreover, when the power supply apparatus disclosed in Patent Publication 1 detects a fault such as short-circuiting of a temperature sensor, it operates a ventilation fan to expel the gas generated by the battery.
In this type of power supply apparatus, if a temperature sensor touches the surface of a battery and short-circuits to it, the temperature sensor is exposed to a high voltage, and is likely to cause failure of the circuit for detecting the electrical resistance of the temperature sensor. This fault can be prevented by isolating the circuit for detecting the electrical resistance of the temperature sensor from the battery. Even with this circuit design, however, if a plurality of temperature sensors short-circuit to the surface of the battery, an overcurrent flows through the circuit including the temperature sensors, causing failure of the circuit including those serially connected temperature sensors.
In a power supply apparatus mounted on a vehicle, it is desirable that, even if one temperature sensor short-circuits to a battery and makes the detection of the battery temperature partially impossible, other temperature sensors, i.e., those which are not short-circuited to the battery, be able to continue detecting the battery temperature. That is, what is important here is that the vehicle can keep running.